i) Field of the Invention
This invention relates to a panel member for use in an overhead door assembly, to an overhead door assembly incorporating such a panel member and to an improved overhead door incorporating such a panel member.
ii) Description of Prior Art
Overhead doors employed in warehouses have a plurality of generally rigid panels arranged in a vertical linear array in which the edges of adjacent panels are flexibly coupled by hinges. The flexible coupling permits the door to be moved from a vertical orientation adjacent the door opening, which configuration closes the door opening, to an overhead horizontal configuration in which the door opening is open, along a pair of parallel tracks located at the sides of the door opening.
The parallel tracks include a vertical section adjacent the door opening, and an upper inclined or horizontal section with an intermediate curved or inclined section therebetween.
The door is guided along the tracks by rollers coupled to the door, particularly to the sides of the panels.
Overhead doors of this type are well known and as illustrative thereof there may be mentioned U.S. Pat. No. 974,699, U.S. Pat. No. 3,140,508 and U.S. Pat. No. 4,676,293, the teachings of which are incorporated herein by reference.
U.S. Pat. No. 4,676,293, David H. Hanssen, describes an overhead door of this type and offers a solution to one problem associated with such doors, namely, the problem of damage caused by impact of a moving vehicle, such as a forklift truck, with the door.
The solution in U.S. Pat. No. 4,676,293 is to have a bottom panel of the door detachably mounted, such that upon impact the bottom panel separates from its rollers becoming detached and physically displaced from the parallel tracks.
In practice difficulties are encountered in the practice of U.S. Pat. No. 4,676,293, in restoring the displaced bottom panel into engagement with the tracks and there are also difficulties in restoring the spring tension counterbalance assembly of the door, which may also suffer damage during the displacement of the bottom panel.